Types and functions of Thermostat system

To keep a rigid control over the cooling, therefore, a thermostat valve is used, which automatically keeps the cooling water temperature at a predetermined value. The thermostat is used in engine cooling systems and it is used to maintain a system’s temperature.

Bellows  type

Wax or hydrostatic type

 Bellows type thermostat

          It consists of metallic bellows filled with some volatile liquid like acetone. The valve is fitted in the water hose pipe at the engine outlet. When the engine after starting is warming up, it is desired that the cooling system should not operate so that the engine warms up early. During this period, the thermostat valve remains, closed, because the liquid inside as yet has not changed its state and, therefore, does not exert exert any pressure on the valve.

But as the cooling water temperature reaches a predetermined value, 75-80^oc the liquid inside is converted into vapour which exerts pressure on the valve, which begins to open, so that the water circulation starts. The valve then opens gradually further as the water temperature rises, until it is fully open at about 90-95^oc. Thus the thermostat controls the flow of water through the radiator according to the engine cooling requirements.

Wax thermostat

As the coolant is heated, it transmits its heat to the copper-loaded wax having a high coefficient of thermal expansion which expands so that the rubber plug contracts against the plunger and exerts a force on it upwards so that it moves vertically. This movement of the plunger opens a valve in the thermostat to allow coolant to flow through the radiator.